The radio transmissions of a single base station cover a particular geographical area usually called a “cell.” A change in serving cell occurs as a mobile station (MS or user equipment (UE)) travels from an old cell to a new cell. This permits mobile stations to “roam” considerable distances. In view of the extent to which a UE can travel, a number of geographic area levels are utilized for mobility management. A location area (LA) is a group of cells established by a service operator for circuit-switched connections. A routing area (RA) is a group of cells established by a service operator for packet-switched connections. As the UE moves, it updates its LA and/or RA so the UE can be located within that larger area even when it travels outside of a particular cell. Then, when the network needs to establish a connection or exchange data with a UE and the location of the UE is not known at a cell level, the UE is paged within the last location area or routing area updated by the UE. The UE answers the page by sending a page response message to the network from the particular cell where the UE is currently located.
A UE can change its serving cell (which consequently may be in a different LA or RA) autonomously, using a procedure called reselection. When the UE is in idle mode and is camped normally on a cell, it monitors its neighboring cells for a possible reselection in case one of the neighboring cells provides better service. Alternately, a UE can change its serving cell as directed by the network, using a procedure called redirection. If a reselection or redirection is to a cell in a different LA or RA, a location area update (LAU) or routing area update (RAU) will be needed.
The process of LAU and RAU may take several seconds due to the various authentication and identification procedures that the network may request. If a UE begins to place an emergency call and it then changes tQ a cell in a different LA and/or RA through redirection or reselection, then it will perform a LAU and/or RAU, which may delay placement of the emergency call. Thus, it is desirable to avoid performing location area updates and routing area updates when attempting to place an emergency call.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Drawings and accompanying Detailed Description.